Growth And Characterization Of Gaalas/gaas And Gainas/inp Structures: The Effect Of A Pulse Metalorganic Flow

GaAlAs/GaAs and GaInAs/InP thick layers, single and multiple quantum wells were grown by atmospheric pressure metalorganic vapor phase epitaxy. Auger electron spectroscopy, wedge transmission electron microscopy, x-ray diffraction, low-temperature photoluminescence, and scanning electron microscopy were used to analyze the crystal quality. These analysis techniques show that layers grown using high vapor pressure metalorganic sources present fluctuations in the ternary alloy composition. We propose that these fluctuations are due to the pulse character of the high vapor pressure metalorganic flow. Bubbling experiments were performed to show the relationship between ternary layer composition fluctuation and the pulse character of the metalorganic flow. High vapor pressure metalorganic source like trimethylgallium presents tens of Angströms growth rate per pulse or bubble whereas a low vapor pressure source like triethylgallium presents few Angströms growth rate per bubble.71117918

High spatial resolution picosecond cathodoluminescence of InGaN quantum wells

The authors have studied InxGa1-xN/GaN (x approximate to 15%) quantum wells (QWs) using atomic force microscopy (AFM) and picosecond time resolved cathodoluminescence (pTRCL) measurements. They observed a contrast inversion between monochromatic CL maps corresponding to the high energy side (3.13 eV) and the low energy side (3.07 eV) of the QW luminescence peak. In perfect correlation with CL images, AFM images clearly show regions where the QW thickness almost decreases to zero. Pronounced spectral diffusion from high energy thinner regions to low energy thicker regions is observed in pTRCL, providing a possible explanation for the hindering of nonradiative recombination at dislocations. (c) 2006 American Institute of Physics

Local quantification of the composition in GaAs/AlxGa1-xAs structures by thickness fringe analysis

The increase of the complexity in semiconductor structures raises more and more the need for local evaluation techniques. For example, laser structures with graded-index waveguides are now widespread, but the characterisation of the shape of the gradient is still empirical. In this study, we use transmission electron microscopy (TEM) for the local determination of the chemical composition of GaAs/AlxGa1-xAs semiconductor laser structures, by quantifying the variation of the thickness fringe profiles with the aluminium content on wedge shaped samples. Contrary to former studies, the presented method uses experimental profiles for calibration. The quantification procedure is thus greatly simplified since no simulation program is needed. Measurements can be performed over distances of more than 1 mu m with a spatial resolution of 1 nm, at any depth of the sample. The precision obtained is about +/-0.03 for the aluminium content x, and the results show the potential of the method for the assessment of semiconductor layer structures

Quantitative analysis of electron-beam-induced current profiles across p-n junctions in GaAs/Al0.4Ga0.6As heterostructures

We propose a method for the quantitative evaluation of electron-beam-induced current profiles measured in normal-collector geometry across p-n junctions in GaAs/Al0.4Ga0.6As heterostructures. We obtain a theoretical expression, valid for all distances from the junction, and which takes into account the spatial extension of the electron-hole pairs generation. From the comparison of calculated with experimental profiles, we evaluate the minority carrier diffusion length and to some extent the surface recombination velocity. (C) 1996 American Institute of Physics

Characterization of semiconductor sub-micron gratings: Is there an alternative to scanning electron microscopy?

The characterization of sub-micron gratings is usually performed on scanning electron microscopes, although the dimensions of the features often make the observations difficult. We report here on a new method applicable to III-V and II-VI semiconductors: we use transmission electron microscopy on wedge-shaped samples oriented along a [111] zone axis. Grating parameters can be obtained with a precision of 1 nm, along with information on the shape and the regularity of the ridge profile, the surface quality as well as the local chemical composition

Fluorescence quantum yield and lifetime of 'red' polydiacetylene chains isolated in their crystalline monomer matrix

The fluorescence yield, eta approximate to 0.30, and Lifetime, tau approximate to 52 ps, of recently discovered 'red' polydiacetylene isolated chains [R. Lecuiller, J. Berrehar, C. Lapersonne-Meyer, M. Schott, Phys. Rev. Lett. 80 (1998) 4068] have been measured at 15 K. These values show that the relaxation scheme of the 'red-chain' exciton is very different from that of the usual 'blue chains', and that excited states of A, symmetry are not present in the optical gap of red chains. Moreover, the radiative lifetime is very short at tau(rad) approximate to 170 ps. (C) 1999 Elsevier Science B.V. All rights reserved

High-reflectance GaInP/GaAs distributed Bragg reflector

A high-reflectance GaInP/GaAs distributed Bragg reflector (DBR) was grown by chemical beam epitaxy (CBE). The mirror consists of 40 pairs of alternating layers and was designed for a centre wavelength of 980 nm, resulting in a total thickness of 5.8 mum. Highly stable growth conditions led to a maximum reflectance of 0.99 and to a variation in the centre wavelength of only 5 nm over the 2'' (50.8 mm) wafer. Transmission electron microscopy and X-ray diffraction measurements confirmed the vertical uniformity and the crystallographic quality of the sample